The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-264173 filed on Sep. 10, 2002, the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection system and fuel injecting method for an internal combustion engine, and more particularly to a fuel injection system in an internal combustion engine in which respective fuel injection valves on the upstream and downstream sides have been arranged with a throttle valve interposed therebetween.
2. Description of Background Art
When the fuel injection valve is provided upstream from the throttle valve, the volumetric efficiency is improved because heat is taken from intake air when injection fuel vaporizes. Therefore, the engine output can be increased as compared with when the fuel injection valve is provided downstream from the throttle valve.
When, however, the fuel injection valve is provided on the upstream side, a response lag occurs in fuel transport as compared with when the fuel injection valve is provided downstream from the throttle valve. This response lag occurs because the distance between the upstream side fuel injection port and a combustion chamber inevitably becomes longer.
There has been disclosed in, for example, Japanese Patent Laid-Open Nos. 4-183949 and 10-196440, a fuel injection system in which fuel injection valves have been provided upstream from and downstream from the intake pipe respectively with the throttle valve interposed therebetween in order to improve the engine output and cope with the response lag.
FIG. 11 is a cross-sectional view showing a major portion of an internal combustion engine in accordance with the background art in which two fuel injection valves have been arranged, and with the throttle valve 52 of the intake pipe 51 interposed, there have been arranged a first fuel injection valve 50a on the downstream side and a second fuel injection valve 50b on the upstream side.
When protecting an engine mounted with an electronic-controlled fuel injection valve thereon from over-speed, when restricting the engine output to an upper limit value, or when restricting the speed of a vehicle mounted with the engine concerned thereon to an upper limit speed, there has been known a technique for prohibiting an operation of the fuel injection valve or interrupting fuel supply by replacing with the thinned-out injection.
In an engine in which fuel injection valves have been provided on the upstream side and on the downstream side respectively with the throttle valve interposed therebetween, however, the distance between the fuel injection port of the fuel injection valve provided on the upstream side and the cylinder becomes far to cause a response lag. As a result, a so-called overshoot occurs, in which even though fuel injection may be restricted after it is detected that the process values such as the engine speed and the vehicle speed have reached the upper limit, these process values exceed the upper limit values. For this reason, in an engine equipped with the upstream fuel injection valve and the downstream fuel injection valve, the upper limit value had to be set to be lower than the original upper limit value.
It is an object of the present invention to solve the problem of the conventional technique described above, and to provide a fuel injection system for an internal combustion engine which has been arranged in such a manner that process values such as the engine speed, the vehicle speed or the engine output are accurately restricted at the upper limit values.
In order to achieve the above-described object, the fuel injection system for an internal combustion engine of the present invention is equipped with an intake pipe equipped with a throttle valve, an upstream fuel injection valve provided upstream from the throttle valve and a downstream fuel injection valve provided downstream from the throttle valve, and includes the following novel aspects:
According to a first aspect of the present invention, the fuel injection system is provided with means for detecting process values representing an operating state and a traveling state of the internal combustion engine, and means for restricting fuel injection due to each of the fuel injection valves when the process values have reached predetermined upper limit values, wherein the upper limit values are caused to differ between the upstream fuel injection valve and the downstream fuel injection valve.
(2) According to a second aspect of the present invention, the fuel injection system includes means for detecting process values representing an operating state and a traveling state of an internal combustion engine; means for detecting whether or not the process values have reached quasi-upper limit values at this side of predetermined upper limit values; means for restricting, when the process values reach the quasi-upper limit values, fuel injection due to the upstream fuel injection valve; and means for restricting, when the process values reach the upper limit values, fuel injection due to the downstream fuel injection valve.
According to the first aspect (1) of the present invention, since it is possible to stop the upstream fuel injection valve and the downstream fuel injection valve at different times, if the stop timing is set in accordance with relative positional relationship of both valves, it will become possible to arbitrarily adjust fuel distribution within the fuel injection area.
According to the second aspect (2) of the present invention, since in an upward course of the process values, fuel injection due to the upstream injection valve can be stopped earlier than the downstream injection valve, it is possible to prevent the overshoot of the process values resulting from the response lag in the upstream injection valve.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.